When one unintentionally uses a phrase or conversational tangent that has no relation to the subject matter preceeding it. See Non Sequitur.

Ken: So then she put down the remote, and we had a fight.
Kane: Over what, exactly?
Ken: You know how you forget to put the toilet seat down? Well, I fed a squirrel a chilli yesterday. Comedy gold.
Kane: Whoa. That's one heck of a non sequifuck there, mate.